1. Field of the Invention
The present invention relates to devices used to separate fluids and solids, and more particularly to vessels used to remove solids from water and oil extracted from a well bore.
2. Description of Related Art
When a well has been completed in a productive formation, a mixture of reservoir fluids enters the well bore and is brought to the surface. The reservoir fluids are lifted by either internal reservoir pressure or pumps, and they contain crude oil, natural gas, produced water, and solids. The solids are generally sand and silt from the reservoir formation, and will be collectively referred to herein as “solids”. The first step in the production process involves separating the oil, gas, and water into different streams where they can be managed appropriately. This is typically accomplished by gravity separation in a horizontal or vertical separation vessel.
In the typical horizontal three-phase separation vessel, gas rises to the top where it exits the vessel and can be collected for later processing and sale. Because the specific gravity of the oil is less than that of the water, the oil layer floats on top of the water layer. Using weirs or other means, the oil is collected in an internal oil container or “oil bucket”, while the water is separately collected in another internal container or volume within the vessel. Both the oil and water are removed from the vessel through their respective outlets.
During the separation and removal of the oil, water, and gas, the sand is allowed to settle on the bottom of the vessel. However, the presence of solids is detrimental to the separation process, because it is highly abrasive, and its accumulation causes flow restrictions for the water and oil within the vessel. Therefore, periodic removal of the solids is required.
In existing separation vessels, solids removal requires that the inlet flow of well bore fluids be diverted from the vessel to another separation device, and all oil and water removed. This diversion of inlet fluids and cessation of separation activities is often referred to as a “shut-in” period. During the shut-in period, the vessel is opened, and a worker enters the vessel to apply pressurized water to the solids to dislodge it and discharge it from the vessel through the existing drain outlet. In most cases, portions of the solids are solidified, requiring the worker to chip away at the solids before they can be washed out of the vessel. Working conditions within the vessel are understandably poor, considering that there is little to no air flow in the presence of potentially toxic hydrocarbon fumes. Additionally, the space within the vessel is cramped, and the temperatures inside the vessel can be uncomfortably hot in the summer months. Moreover, this laborious process can take several days, resulting in additional risks to the worker, liability for the oil company and service companies, labor costs associated with the solids removal, and a loss of revenue during the shut-in period.
Given the disadvantages of the shut-in period and the difficulties of solids removal, attempts have been made to reduce the shut-in time and facilitate solids removal. One such attempt is disclosed in U.S. Pat. No. 6,021,787, and uses a nozzle inserted through an outlet on the vessel. A displacement liquid, such as water, is supplied through the nozzle while the nozzle is manipulated remotely to direct the liquid to areas of concentrated solids. Ideally, the nozzle causes the solids to be dislodged and moved toward other outlets where they can be discharged from the vessel. Similar technology described in U.S. Pat. No. 5,876,512, was also an attempt to remove solids by insertion of a lance through the outlet of the vessel. While effective to some extent, these practices have not provided sufficient removal of the solids. Additionally, because these methods are performed without shut-in, the action of the nozzle tends to cause turbulence in the water and oil, thus increasing emulsions and decreasing production efficiency.
Another effort to remove solids, described in U.S. Pat. No. 7,210,488, that has become common in the oil service industry, is to install one or more high-pressure spraying manifolds within the vessel having a number of conduits and jetting nozzles. Installation of the spraying manifolds requires a one-time shut-in, after which the spraying system can be used many times. However, each time the spraying system is operated, the inlet fluids must be temporarily diverted. The spraying manifolds are generally constructed from plastic, such as polyvinylchloride (PVC) pipe. The manifolds are supplied by one or more flexible hoses connected between the manifolds and internal fittings mounted on the manway cover on the vessel. Water supply hoses are connected to external fittings on the manway cover, and the spraying system is operated until most of the solids are dislodged and removed from the vessel.
While the spraying system, by itself, is intended to reduce the shut-in time and worker effort, the system has proven to be insufficient in many instances. Specifically, about 10% to 20% of the solids often remains in the vessel, because the solids have solidified on the bottom surfaces. Thus, even after the spraying process has been applied, workers are often required to enter the vessel and manually dislodge the solids so that they can be removed. Furthermore, although the shut-in time is substantially reduced in comparison to other methods, it is still desirable to minimize or eliminate the diversion of inlet fluids from the vessel.
Consequently, there is a need for an improved solids removal system which is more effective in dislodging solids from the internal vessel surfaces. Such a system should also enable dislodging and movement of the solids toward an outlet while the separation vessel is actively separating the oil from the water. Most importantly, the solids removal system should require no diversion of inlet fluids from the vessel, no shut-in, and no need for workers to enter the vessel to manually remove the solids.
Optionally, the improved solids removal system herein may be used in combination with the spraying system described above. If the spraying system is used in conjunction with the invention, the novelty and advantages of the invention are still realized, because no workers are required to manually dislodge the solids.
It is believed that the apparatus and method described and claimed herein directly addresses this need.